The present invention relates to polyurethane foam. More particularly the invention relates to a process of producing foam-in-foam polyurethane foam buns and to articles of manufacture produced from such foam-in-foam polyurethane foam buns. According to the present invention, pre-existing shredded and/or ground polyurethane foam particles are bonded together with new polyurethane foam in an improved process to make polyurethane foam buns.
Rebonded polyurethane foam has been made in the prior art by shredding and/or grinding waste polyurethane foam to form polyurethane foam particles, mixing the polyurethane foam particles with a binder, and then curing the binder either at atmospheric pressure, or under reduced pressure, with or without added heat energy, for effecting cure of the binder. The resultant foams have normally had relatively high and nonuniform densities and, because of the appearance of the product, have been used primarily where the foam is not readily seen as, for example, as carpet underlay and the like. When fabricating rebonded foam it was possible to incorporate only relatively low amounts of liquid and solid materials into the foam to modify the foam structure, including the addition of only low amounts of combustion retardant materials to render the resultant foam combustion retardant. If larger amounts of solid and liquid materials were added, the resultant foam would have poor physical characteristics. Accordingly, such rebonded foam could not be used where flame or combustion retardant materials were required.
More recently it has been discovered that shredded and/or finely ground polyurethane foam could be used in making polyurethane foam buns or slabs having relatively high amounts of solid materials by foaming particles of existing polyurethane foam and solid particles of an additive, including fire retardant materials, with new polyurethane foams. Thus, U.S. Pat. No. 4,438,221 describes the preparation of foam-filled foam structures obtained through the steps of admixing particles of flexible polyurethane foam with a solid material, uniformly applying to the mixture a liquid, flexible polyurethane foam-forming material containing a reactive polyol and a polyisocyanate, and foaming the foam-forming material with water to provide a flexible foam having bonded therein the polyurethane foam particles and solid material. According to the teaching of the U.S. Pat. No. 4,438,221, it was possible to incorporate relatively large amounts of solid materials into the polyurethane foam particles while maintaining the integrity and good physical properties of the foam structures. U.S. Pat. No. 4,438,220 also describes foam-filled polyurethane foam structures of the type described in the U.S. Pat. No. 4,438,221. In the U.S. Pat. No. 4,438,220 the solid materials which are incorporated are specifically combustion retardant materials to provide polyurethane foam structures having enhanced combustion retardant characteristics. Each of the aforesaid patents, i.e., U.S. Pat. Nos. 4,438,220 and 4,438,221, is assigned to Wm. T. Burnett & Co., Inc., the assignee of the present application.
Although the aforesaid patents describe new compositions of matter and methods of making foams which are highly meritorious, an improved method of making foam-in-foam buns or slabs having a high solids content, and controlled density is still desired. The density control is particularly difficult when using high amounts of solid materials in the foam formulation.